class ThreeParameterLogistic:
  def __init__(self, model_params, kwargs):
    self.model_params = model_params
    # check if exists, if not error out
    self.b_param = kwargs['b_param']
    self.e = 2.71828
    self.theta = kwargs['theta']

  # contains the primary 3pl function, determining the probably of an inidividual
  # that an individual at a certain theta would get a particular question correct
  #  detailed further on page 161, equation 1 here:
  # https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5978482/pdf/10.1177_0146621615613308.pdf
  def result(self):
    a = self.model_params.a_param
    c = self.model_params.c_param
    return c + (1 - c) * (1 / (1 + self.e**(-a * (self.theta - self.b_param))))